1,720,955 research outputs found
Thermo-Osmosis: Theory and Simulations
Full text linkThermal gradients lead to macroscopic fluid motion if a confining surface is present along the gradient. This fundamental nonequilibrium effect, known as thermo-osmosis, is held responsible for particle thermophoresis in colloidal suspensions. A unified approach for thermo-osmosis in liquids and in gases is still lacking. Linear response theory is generalized to inhomogeneous systems, leading to an exact microscopic theory for the thermo-osmotic flow, showing that the effect originates from two independent physical mechanisms, playing different roles in the gas and liquid phases, reducing to known expressions in the appropriate limits. This theoretical approach, as well as the problem of the definition of the transport coefficient in bidimensional systems, is also studied from a numerical point of view, exploiting the Molecular Dynamics technique
Thermal Forces from a Microscopic Perspective
No full textThermal gradients lead to macroscopic fluid motion if a confining surface is present along the gradient. This fundamental nonequilibrium effect, known as thermo-osmosis, is held responsible for particle thermophoresis in colloidal suspensions. A unified approach for thermo-osmosis in liquids and in gases is still lacking. Linear response theory is generalized to inhomogeneous systems, leading to an exact microscopic theory for the thermo-osmotic flow, showing that the effect originates from two independent physical mechanisms, playing different roles in the gas and liquid phases, reducing to known expressions in the appropriate limits
Dinamica microscopica di gel fisici : un sistema colloidale modello
No full textLAUREA MAGISTRALELa possibilità di regolare il potenziale d'interazione tra le particelle è una delle caratteristiche più interessanti dei sistemi colloidali. Nella mia tesi, ho considerato una tipologia particolare di particelle, costituite da un polimero fluorurato e stabilizzate stericamente da catene polimeriche, legate alla loro superficie. Tali catene schermano le forze attrattive di van der Waals tra le particelle, impedendo che esse aderiscano. L'affinità con l'acqua di questo strato stabilizzante peggiora alzando la temperatura, e ciò permette d'introdurre forze attrattive regolabili tra le particelle. A T sufficientemente elevata, tali forze attrattive diventano così intense da indurre una separazione in una fase ricca ed in una povera di particelle. Però, a causa del corto raggio d’interazione di tali forze, il processo di separazione di fase viene arrestato, e il sistema si ‘congela’ formando un solido soffice, con le proprietà di un gel ‘fisico’, ovvero un reticolo disordinato dove l’energia di legame tra le particelle è dell’ordine di kBT. I gel fisici sono caratterizzati da una dinamica microscopica spazialmente eterogenea e temporalmente intermittente, che porta a forti effetti ristrutturativi spontanei. Per investigare questo complesso comportamento dinamico, ho sfruttato una nuova tecnica ottica, la Photon Correlation Imaging (PCI), che combina le potenzialità delle tecniche di scattering alla risoluzione spaziale della microscopia ottica. Inoltre, ho sviluppato un algoritmo per ottenere il grado di correlazione temporale della dinamica, spazialmente risolto. In questo modo ho potuto rivelare la presenza e investigare le caratteristiche di improvvisi riarrangiamenti strutturali. L’intervallo temporale tra due di questi ‘micro-terremoti’, che iniziano da una certa regione del gel per poi espandersi rapidamente in tutto la struttura, aumenta come una legge di potenza dell’età del gel. Le evidenze riscontrate sono coerenti con un modello in accordo col quale i riarrangiamenti nel gel sono causati dall’improvviso rilascio di stress localizzati, generatisi durante il rapido processo di separazione di fase.The possibility of tuning the interparticle interaction potential is one of the most interesting features of colloidal systems. In my thesis, I have considered a special kind of colloidal particles, made of a fluorinated polymer and sterically stabilized by surface-bonded polymeric chains, which shield the van der Waals attractive forces between the particles, preventing them from sticking. Yet, the affinity for water of the stabilizing layer worsen by raising the temperature, and this allows to introduce tunable attractive interparticle interactions. At sufficiently high T, these attractive forces become so strong that a phase separation in a particle-rich and a particle-poor phase takes place. Due to the short-range nature of the attractive forces, however, the phase separation process gets arrested, and the system ‘freezes’ into a tenuous solid with the properties of a ‘physical’ gel, namely a disordered network where the interparticle bond energy is of the order of kBT. Physical gels are characterized by a spatially heterogenous and temporally intermittent microscopic dynamics leading to strong spontaneous restructuring effects. To investigate this complex dynamics, I have exploited a novel optical technique, Photon Correlation Imaging (PCI), which combines the power of scattering methods with the spatial resolution of optical microscopy, and I developed a suitable algorithm to extract the spatially-resolved degree of dynamic temporal correlation. This approach allowed me to highlight the occurrence and investigate the features of sudden structural rearrangements. The time interval between two of these peculiar ‘micro-quake’ events, which start from a given location in the gel and rapidly span through the whole gel, increases as a power law of the gel aging time. This evidence is consistent with a model where the gel rearrangement is caused by the sudden release of local stresses that get frozen in by the rapid phase separation process
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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